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Well-differentiated Neuroendocrine Tumor

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Well-differentiated neuroendocrine tumors (WDNETs; Carcinoids) comprise 20% of all gastrointestinal neoplasms and about 6% of all colorectal neoplasms. The median age at diagnosis is 6th to 7th decades of life with a female predominance.

Locations: According to the SEER database, the most common locations for NETs of gastrointestinal tract among patients in the US are: small intestine (38%), rectum (34%), colon (16%), stomach (11%), and unknown sites (1%).

Clinical: About 50% of WDNETs of large bowel are small lesions discovered incidentally on colonoscopy done for other reasons. Large bulky tumors may present with abdominal pain, obstruction, anorexia, weight loss, rectal bleeding, and diarrhea. Carcinoid syndrome is quite rare even with liver metastases.

This colonoscopic image shows a small polypoid lesion with smooth overlying mucosa discovered incidentally in the rectum. It was diagnosed as a WDNET (carcinoid). Image courtesy of: @PatholWalker

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